Defense Grid — ruling 1

In Two-Headed Giant, spells don't cost extra on your own turn.

Defense Grid — ruling 2

The additional cost can be reduced by effects that reduce costs, such as Sapphire Medallion.

Defense Grid : règles, fonctionnement et interactions (MTG)

Defense Grid is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Each spell costs more to cast except during its controller's turn.

How it works : Defense Grid

Original English text — Wizards of the Coast / Scryfall

#1May 1, 2006· Wizards of the Coast
In Two-Headed Giant, spells don't cost extra on your own turn.
No other card is named in this ruling.
#2October 4, 2004· Wizards of the Coast
The additional cost can be reduced by effects that reduce costs, such as Sapphire Medallion.
No other card is named in this ruling.